For more than 80 years, the Thomas family has lived on a farm that abuts three pits containing 6.1 million tons of ash from the coal-fired boilers of Duke Energy's Buck Steam Station. Built in 1926, the plant towers over the Yadkin River an hour's drive from the Charlotte headquarters of the nation's largest electricity company.

Since 2011, Duke and North Carolina environmental regulators have known that groundwater samples taken from monitoring wells near the Thomases' home and others in Dukeville contained substances -- some that can be toxic -- exceeding state standards.

The state could have required Duke to implement a cleanup plan to prevent spreading contamination. That never happened, state regulators said, because they weren't certain whether coal ash production was to blame or if the substances were naturally occurring.

Those living near the plant were never warned and continued using their well water for drinking, bathing and cooking. Now the Thomases and their neighbors wonder not only what's in their water, but whether it's harmed them or their children.

In the wake of a massive Feb. 2 coal ash spill at another Duke plant, state regulators, environmental activists and Duke officials have been testing the water supplies for some of the 150 homes in Dukeville.

Both the state and Duke said their own tests found no significant problems. However, the environmental group Waterkeeper Alliance said its tests show levels of some potentially toxic substances above state standards.

"I feel like we're due answers," said resident Sherry Gobble. "I'm not pointing the finger at Duke. I just need to know my children are safe."

Coal ash is the byproduct left behind when coal is burned to generate energy. It contains substances including arsenic, selenium, chromium, beryllium, thallium, mercury, cadmium and lead.

Though there are no known studies linking coal ash pits to adverse health effects, residents here are worried nonetheless because of years of cancer diagnoses and other ailments.

In the Thomas family, Joanne says she had a pituitary tumor removed from the base of her brain in 1996. Her husband, Ron, long retired from a job where he worked with industrial chemicals, survived prostate cancer and is undergoing treatment to remove mercury, cadmium and selenium from his blood. Records show one of Ron's brothers died of a brain tumor at 51. Ron's great nephew died of brain cancer at 37. Both lived in Dukeville.

Duke officials said they have seen no evidence those living near its ash pits are at any risk, and insist the groundwater is flowing away from neighboring properties.

"If we had any indications that we see with concerns to your health, Duke Energy would be proactive," Duke spokeswoman Erin Culbert told residents who gathered for a meeting in May.

The February spill at Duke's power plant in Eden, 80 miles northeast, coated North Carolina's Dan River in toxic sludge and ignited debate about the safety of Duke's 33 coal ash dumps across the state. The three pits at Buck are ringed by 14 monitoring wells that are sampled three times a year and tested for contamination by Duke.

Since 2011, according to sampling results released by the N.C. Department of Environment and Natural Resources under a public records request, the wells exceeded state groundwater standards on 226 readings out of more than 2,500, most commonly for high amounts of manganese and iron but also for some boron.

One monitoring well, located about 20 feet from the Thomas property line, exceeded groundwater standards for chromium on all three tests in 2011. Chromium in its most toxic form -- called hexavalent chromium -- is a known carcinogen.

In March, April and May, the Waterkeeper Alliance took samples from 15 wells in Dukeville and from seepage on the Thomas family's land. According to lab reports provided to the AP:

-- Water from the Thomases' kitchen faucet contained chromium at nearly four times the state limit for groundwater and exceeded the state limit for arsenic.

-- Samples taken from the wellhead at the Thomas farm and 14 other wells contained some hexavalent chromium, though at amounts considered acceptable by state regulators. Some wells also exceeded state groundwater standards for total chromium, lead, iron and manganese.

-- A sample taken from water seeping up in the Thomases' cow pasture contained chromium at nearly 10 times the state groundwater standard, lead at more than six times the standard, manganese at 562 times the standard, iron at 1,086 times the standard and boron at 1.5 times the standard.